Coding and marking printing system includes in one form inkjet coding which falls into two main types. One being DOD (Drop on Demand) and the other is CIJ (Continuous Ink Jet). Drop on demand includes valve based and piezo-electric based systems.
Generally DOD systems have a matrix print generation with a fixed spacing in both the X and Y axes and utilising as the nozzles, a series of in-line plungers, valves or solenoids. Nozzles are either lined up vertically or placed on a fixed angle dependent on size of characters or indicia being printed. The nozzle arrangement is typically a 7, 16 or 32 valve print head. The dot matrix format used to create each character is as little as 5×5 dots up to possibly as many as 32×24 dots. The more dots in each character the better the print quality or “resolution”. Due to the dot matrix format of the characters, there is a limit as to what can be printed with the DOD systems that uses a valve, plunger or solenoid type arrangement in-series (fixed spacing) as the nozzles. If they are extremely complex graphic characters, or require high quality, high-resolution printing, then the DOD ink jet printers may not be suitable.
Therefore major drawbacks with known drop on demand printing systems include the fixed spacing and limited dots and fixed size of image, which cause a very restricted dot matrix image with low resolution and not a pleasing effect.
Current methods for driving DOD print head nozzles is in the form of plunger, valves or solenoid in plunger or valve systems and the controlling systems includes hard driving of the plunger/valves/solenoids, by an initiating control. Each valve in the print head is controlled with an On/Off or a common stepped voltage according to a regular pulsed position output. This method of driving can reduce the life of the plunger/valve/solenoid and require larger circuits that use more power and produce more heat. This is a form of stepping the power supply that is feeding the print head, but not stepping the voltage feeding the jets themselves.
By using this method, you are limited to printing in columns only and if the print head is placed on an angle to produce a smaller print height it is possible to introduce a wave into the information printed. This happens because the current systems can only place a dot when the power supply produces the step voltage and the spacing that has been selected.
Therefore substantial restrictions of such systems include the resolution equations for these systems as well as the time to print the image. The more dots per character or image, the slower the printer has to print. The DOD printers produce each dot in turn and therefore if the matrix was a 32×24 as compared to a 5×5, the printer requires 5 times or more time to produce each character in the 32×24 format, thus reducing the overall print speed capabilities.
Traditionally DOD printing technologies cannot print at the same speeds of the CIJ (up to 7.2 m/s). The current DOD systems can only print at speeds of up to 4 m/s. This is due to the processor that is doing the print generation is also initiating the opening and closing of each jet. This takes a lot of effective bandwidth away from the processor, so as the print speed increases the processor bandwidth requirements increase accordingly. Also as the processor bandwidth increases, the DOD print controller and/or controlling system can no longer ensure that the placed dot is of the correct size and placed precisely in the correct position. This causes the print to eventually become illegible.
Therefore a further limitation is the speed and resolution quandary that provides an unacceptable processor limitation in the modern printing industry and an unacceptable heat problem in the solenoids.
The DOD system consists of a pressurized pot of ink or ink pump, which is connected to each nozzle via a manifold and solenoid. These solenoids are then controlled by a print controller, which produces an open or closed situation to allow droplets of ink to be projected from the nozzles at the appropriate time within the restriction of resolution of the regular pulsed position output. The solenoid can either directly control a valve or a print wire is used. In the case of print wire a piece of wire open and closes a port on the print head surface. This wire is controlled via a solenoid. The print wire method cannot print at the same speeds of the directly controlled valve.
A further problem exists in the blockage of the nozzles when idle for a certain time. Generally the longer the idle time, the greater the blockage and the more ink flow pressure required to clear the blockage. However current systems only have an initial start blockage clean.
It is an object of the invention to provide an improved drop on demand printing system that overcomes or at least ameliorates one or more of the problems of the prior art and allows for more detailed definition of image.